EF代码优先 - 用外键选择

获得我认为是EF中一个奇怪的行为，我希望有人能够阐明一些。基本上，如果我用外键检索一个项目，外键项目不被检索？这似乎有点短暂。我是否错过了一些显而易见的内容，或者是否存在处理这种问题的模式EF代码优先 - 用外键选择

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Data.Entity; 

namespace EFTest 
{ 
    class Program 
    { 
     static void Main(string[] args) 
     { 
      Database.SetInitializer(new MCInitializer()); 

      EFTestEM context = new EFTestEM(); 
      var foos = from m in context.Foo 
        select m; 

      foreach (var foo in foos) 
      { 
       // foo.MyBar is null?! How do I populate it? 
       Console.WriteLine("{0},{1}",foo.Desc,foo.MyBar.Whatever); 
      } 

     } 

    } 


    [Table("tbl_Bar")] 
    public class Bar 
    { 
     [Key,DatabaseGenerated(DatabaseGeneratedOption.Identity)] 
     public int BarId { get; set; } 
     public string Whatever { get; set; } 
     public string Whenever { get; set; } 
    } 


    [Table("tbl_Foo")] 
    public class Foo 
    { 
     [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)] 
     public int FooId { get; set; } 
     public string Desc { get; set; } 
     public int MyBarId { get; set; } 
     [ForeignKey("MyBarId")] 
     public Bar MyBar { get; set; } 

    } 

    public class MCInitializer : DropCreateDatabaseAlways<EFTestEM> 
    { 
     protected override void Seed(EFTestEM context) 
     { 
      List<Bar> bars = new List<Bar> 
          { 
           new Bar(){Whatever = "Bar1"}, 
           new Bar(){Whatever = "Bar2"}, 
           new Bar(){Whatever = "Bar3"}, 
          }; 


      List<Foo> foos = new List<Foo> 
          { 
           new Foo() {Desc = "Foo1", MyBar = bars[0]}, 
           new Foo() {Desc = "Foo2", MyBar = bars[1]}, 
           new Foo() {Desc = "Foo3", MyBar = bars[2]} 
          }; 

      foreach (var bar in bars) 
       context.Bar.Add(bar); 
      foreach (var foo in foos) 
       context.Foo.Add(foo); 

      context.SaveChanges(); 

      base.Seed(context); 

     } 
    } 
}

来源

2012-11-15 Martin Clarke

对于延迟加载，您需要将相关属性设置为虚拟。

E.g.

public virtual Bar MyBar { get; set; }

来源

2012-11-15 16:46:11 Charlino

相关属性需要'急切加载'或'延迟加载'（请参阅Charlino的回答）。

急切地加载，代码需要利用“包括”延伸：

 var foos = from m in context.Foo.Include("MyBar") 
       select m;

的

来源

2012-11-15 20:26:29

EF代码优先 - 用外键选择

回答

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